1. Field of the Invention
This invention relates to time change or moving target indication signal processing and particularly to a processing system utilizing charge-coupled devices to provide simplified, accurate and highly reliable processing.
2. Description of the Prior Art
Frame-to-frame subtraction concepts for performing MTI (moving target indication) with either visible or infrared detector arrays such as staring electro optical sensors, have previously required a separate analog or digital memory to store the first field prior to the readout and subtraction from the second field. The conventional subtraction arrangement has a limited accuracy because all signals do not follow the same electronic paths and because of the limited bandwidth. A moving target indication system that compares one field to the other of the scene being interrogated by transferring the signals through essentially a common path of storage elements would provide an arrangement that develops a highly accurate difference value with a minimum of equipment.
SUMMARY OF THE INVENTION
The moving target indicator (MTI) processing system of the invention loads successive integrated samples, each representing a different time field, from individual detectors into adjacent CCD (charge-coupled device) storage buckets and then clocks them to a suitable output device for developing difference signals between the different fields from each detector. The output device may be a CCD differencing circuit or a differential amplifier either of which samples the charge stored in adjacent CCD buckets and gives an output proportional to the difference. The system allows the successive signals from individual detectors to pass through virtually identical elements in the signal processing chain thereby reducing the effects of transfer ineffeciencies on the accuracy of the differencing or MTI process and permitting high subtraction accuracies. In one arrangement, in accordance with the invention, the processing is performed on the focal plane and in the second arrangement the processing is performed off the focal plane allowing the detectors to be sampled at a rate which is much higher than the system field time. The high signal bandwidth permits additional signal processing to be performed before subsequently integrating the samples and performing the differencing. In the off-focal plane arrangement the signals which represent sub-fields from a row or plurality of rows of detectors are shifted in parallel into a CCD multiplexer and are read out through the intermediate signal processing into an off focal plane CCD register of similar construction. The sub-field signals are then shifted in parallel into storage registers which integrate successive input sub-field samples for a field time. After both fields are integrated, the contents of the integrating registers are read out through the differencing arrangement to provide the difference or MTI signals.
It is therefore an object of this invention to provide a simplified and highly accurate time change or moving target indicator system.
It is another object of this invention to provide a moving target indicator system utilizing CCDs for use with staring electro optical sensors.
It is a further object of this invention to provide moving target indicator systems that may be utilized either on the detector focal plane or partly off of the detector focal plane.
It is still another object of this invention to provide a moving target indication concept utilizing charge-coupled devices that provides a high signal bandwidth for signal processing.
It is another object of this invention to provide a CCD MTI system that is compatible with other CCD processing and signal handling devices.